Thermionic cathode



July 30, 1935. c, UND

THERMIONIC CATHODE Filed April 5, 1930 Illlllllll/l/l/llllfllllllll l lilfi Inventor Clifton G. Tound,

His 'Attovneg.

Patented July 30, 1935 t UNlTED STATES PATENT OFFICE THERMIIONIC CATHODE Clifton G. Found, Schenectady, N. Y.,assignor to General Electric Company, a corporation or New York Application April 5, 1930, Serial No. 441,986

8 Claims. (Cl. 176-126) The present invention relates to thermionic are described and claimed in applications Serial cathodes suitable for use in electrical discharge No. 156,713, filed October 9, 1925, and Serial No. devices, for example such as glow lamps. 226,275, filed November 22, 1926 (see correspond- It is one of the objects of my invention to proing British Patents 282,766 and 298,906).

vide thermionic cathodes which are operable with The cathode is mounted in a suitable vitreous 5 a minimum of heating energy and minimum elecenvelope 12, as shown in Fig. 1, being supported trical disintegration. One of the features of my by wires l3 and H, the wire l3 being welded, or improved cathode is its configuration asafunnelotherwise joined, to the conductor 5, and the shaped hollow body. wire l4 being joined to the shell If These wires v The novel features of my invention will be furl3 and M are sealedinto a glass stem l5 and are 10 ther pointed out in in the accompanying claims. joined to the external conductors l6, H. Al- My invention is illustrated in the accompanying though it is desirable that the cathode mounting drawing; Fig. 1 is a plan view of a gaseous glow should be arranged as shown in Fig. l to bring its lamp embodying my invention; Fig. 2 illustrates smaller diameter nearest the discharge and the a modified mounting; Fig. 3 is an enlarged detail discharge opening therein remote from the anode 15 view partly in section of my improved. cathode; so as to cause the discharge to sweep over the and Fig. 4 illustrates a modification which is unsurface of the cathode, such an arrangement need provided with a cover. not be used invariably. An alternative arrange- Referring to the drawing, and in particular to ment is shown in Fig. 2.

Fig. 3, a cathode embodying my invention com- The lamp shown in Fig. 1 also is provided with 20 prises a hollow, elongated shell 1, consisting of anodes l8 and I9, having conductors 20, 2| which suitable sheet material, such as nickel, iron, or are sealed into glass stems 22, 23 of branches 24, other base metal which is coated on its inner sur- 25 of the main envelope extending at right anface with a material 2 of high electron emissivity, gles thereto as illustrated.

25 for example, an alkaline earth material, such as The envelope is exhausted by known approved 25 barium oxide. The outside surface of the cathmethods which are employed in the manufacture ode preferably is shiny. The cathode is mainof a lamp, such as described, and then is charged tained at an operating temperature by a suitable with a suitable luminescent gas or vapor, such as heater various forms of which are known. The neon, helium, mercury vaporor a mixture of particular heater illustrated in the drawing congases, at a desired pressure. A neon filling hav- 30 sists of a wire 3 of tungsten, tantalum, or other g a pressure of about two m of mercury y refractory metal wound on a support 4 of suitable be employed.

refractory insulating material, such as beryllia, A gaseous glow device containing a thermionic thoria, alumina, or magnesia. A conductor 5 electrode oi the form and arrangement herein 85 consisting of molybdenum or tungsten passes shown and described the diameter 01' which inthrough the insulating support I and is electricreases along its major axis is operable at inoally connected to one end of the resistance creased net lighting efflciency and with a longer heater at 6. The opposite end of the heater is life. suitably connected to the shell I as indicated at I. In an electrical discharge device of the charac- 40 The main portion of the shell lwhich is conifer shown positive ions are produced by ionization 40 form or funnel-shaped is provided with end 010- of gas. Some of the positive ions strike the walls sures 8, 9 joined by welding or otherwise to the of the envelope and there combine with electrons main portion. The closure for the large end of and insteadoi becoming normal atoms are conthe shell has an opening III of lesser diameter verted to atoms containing potential energy,

than the diameter of said larger end through which are known as metastable atoms. In col- 45 which an electrical discharge may pass. As liding with a negative electrode, the metastable shown in Fig. 4 the end closure, or cover 9, in atoms give up their energy causing the emission some cases may be omitted. However, its presof secondary electrons, sputtering of the elecence isdesirableas it reduces loss of heat and actrode material. and clean-up of gas. The

tive coating material from the cathode. A surmetastable atoms, however, become inactive or 50 rounding shell ll spaced about the cathode, as are destroyed it such electrode or the space ad-. shown in Fig. 4,-may be employed to conserve iacent to it is irradiated by the electrical disheat in the cathode. charge in the'gas. As a consequence, it the elec- My present invention is an improvement over trode area which is exposed to bombardment by prior inventions made by Albert W. Hull, which metastable atoms also is exposed to radiations 55 of the gaseous discharge, metastable atoms can not exist long enough to produce emission of secondary electrons and other deleterious eii'ects at the electrodes.

The conical shape and the arrangement of the cathode with respect to the anodes as shown in Fig. 1 exposes the exterior surface of the cathode to radiation from the discharge in the gas, thus protecting the cathode from undesired bombardment by metastable atoms.

The form and arrangement of the cathode also exposes it to a maximum extent to the heating eifect of the discharge, thus reducing the heat input required to be furnished by the heater 6. A large portion of the heat imparted by the discharge to a cathode is given up nearest the mouth of the cathode from which the discharge emanates. This part of the cathode will not become overheated as its area and hence also its heat dissipating capacity is larger than the small end of the cathode adjacent the cap 8. The closure 9, with its relatively small opening it, conserves both loss of heat and of active material from the cathode and thereby increases both its heating efilciency and its life. The closeness of the small end 8 of the cathode to the internal heater and its relatively small mass permits it to be heated up rapidly when the lamp is put into operation and thus reduces the initial starting period which is required to bring a portion of the cathode to an electron-emitting temperature in order to start the gaseous discharge.

Broad claims 'to the hollow or cavity cathode construction disclosed herein appear in the copending application of A. W. Hull, Serial No. 156,713, filed December 23, 1926. That application also contains claims relating to the combination of a cathode and heat shielding means. The claims in the present application, therefore, are limited to improvements over the invention described and claimed in the application referred to above.

What I claim as new and desire to secure by 'Letters Patent of the United States is:

1. A thermionic cathode for electrical discharge devices comprising an elongated funnelshaped shell an electronically active coating on the interior of said shell, said shell being open to the exterior at the region of greater diameter and a resistance heater mounted in said shell.

2. In a gaseous glow lamp, the combination of a thermionic cathode comprising an elongated hollow body having one end thereof open and the opposite end closed, the open end being of materially greater cross-section than the closed end, and a coating of material of high electron emissivity on the interior of said body, a separate heater for said cathode, an anode, an enclosing envelope, and a luminosity producing gas therein.

3. In an electron discharge device the combination of a thermionic cathode comprising a funnel-shaped hollow body closed at its small end and open to the exterior at its large end, a coating of material'of high electron emissivity on an interior surface of said body, an electrical heater mounted within said body, an anode remote from said cathode, an enclosure for said electrodes, and a gaseous filling at a pressure at which the heating of said cathode by an ionization discharge in said gas is appreciable.

4.' A thermionic cathode comprising a base metal shell the diameter of which increases along its axis, said shell being closed at the region of smaller diameter and having a relatively small opening at the region of greater diameter, a conductor projecting through said closed end and being insulated therefrom, an electric resistance heater mounted on said conductor within said shell, said heater having one terminal thereof connected to said conductor and the opposite terminal to said shell and a coating of material on the interior of said shell having a materially higher electron emissivity than said shell.

5. In an electrical discharge device a thermionic cathode comprising a funnel-shaped elongated, hollow body having a cover for its wide end, said cover being provided with a restricted opening, a material of high electron emissivity within said body, means for heating said body, an anode remote from said cathode, an envelope, and a charge of gas therein.

6. An electric discharge device containing a gas at a sufficiently high pressure to operate with a positive ionization discharge, and being provided with a thermionic cathode comprising an elongated, hollow body, the interior of which is coated with electron-emitting material, and a separate heater for said hollow body, the diameter of said body increasing along its major axis and havingan opening at the larger end thereof, the heat-dissipating capacity of said larger end being sufilciently great to prevent overheating during operation and the heat-dissipating capacity of the smaller and being such that the period of time required to heat said smaller end to an operating temperature is materially less than the time required to heat the larger end, and an anode remote from said cathode.

7. A gaseous glow lamp comprising an envelope, a charge of neon gas therein at a pressure of about-two millimeters of mercury, an anode, and a thermionic cathode spaced apart therein, said cathode comprising a hollow body, the interior of which is presented to said anode, the diameter of said body increasing along its axis and having an opening at the largerend thereof, the heat-dissipating capacity of saidlarger end being sufficiently great to prevent overheating during operation.

8. A gaseous glow device comprising an envelope, a charge of gas therein, an anode and a 

